The invention is based on a hydraulic multiple-circuit brake system having a multiple-circuit brake amplifier for actuating one open brake circuit and one closed brake circuit, the latter closed brake circuit being disposed functionally subsequent to the open brake circuit, and further having an energy supply apparatus comprising a pump and a reservoir and having a multiple-chambered refill container having a separate refill chamber for each brake circuit. A brake system of this kind is known (German Offenlegungschrift No. 2 825 132).
There are various concepts associated with the use of hydraulic brake force amplifiers. These concepts can be divided up into three categories:
Category 1: Brake force amplifiers having two open brake circuits.
Category 2: Brake force amplifiers having one closed brake circuit and one open brake circuit.
Category 3: Brake force amplifiers having two closed brake circuits.
Included in category 1 are normal external-force means or means in which a switchover device is provided to assure that if the energy supply fails, then one or two closed brake circuits are available for use, so that hard braking is still possible mechanically.
Among category 3 systems, auxiliary plunger pistons or, if the system is combined with an anti-slip braking system, feedback pumps are required for pressure modulation; these additional requirements complicate the system.
Category 2 is a mixture, which in some cases is preferred. Purely external force is disadvantageous in the event of an interruption in the energy supply, since no further braking effect can be generated once the hydraulic reservoir has been emptied.
A further consideration is that in multiple-circuit brake amplifiers, the refill containers are subdivided accordingly, so that each circuit has its own reservoir. Both the energy supply apparatus and the corresponding brake circuit are connected to the chamber associated with the open brake circuit. Should the energy supply fail, for instance because of a leak, then the chamber of the refill container will empty, and that brake circuit then fails as well. A remnant braking effect is then attainable only with the other brake circuit.